P0A0C: High Voltage System Interlock Circuit A Low

The voltage sensed on interlock loop A is too low while the module drives the loop – typically an opened loop or a short to ground. GM documents it codegenau: in its 2016 HPC2 table P0A0C sets when the sensed interlock voltage stays below 30 % of the 5 V test signal in 2 of 2 samples (12.5 ms each) with the 12 V supply above 10.2 V; it is Type A, so the MIL lights after one trip. The 2011 Volt tables used a 10 % threshold. Mercedes-Benz model line 243 stores P0A0C00 in the DC converter and on-board charger as a short to ground in the interlock circuit. The opposite fault is P0A0D. Since the loop guards against live HV parts, the system drops the contactors and the car will not drive on electric power.

Symptoms

• Check engine light (GM Type A) and hybrid/EV warning
• No ready mode, electric drive unavailable
• Charging may be blocked

Most likely causes

• HV connector, cover or service disconnect open, interrupting the loop
• Interlock wire shorted to ground, e.g. chafed at a module or the body
• Corroded or pushed-back interlock pins
• Faulty interlock source or sense stage in the battery or hybrid module

What to check, in order

Start with the simplest. You can tick off each step.

1. Read the codes with a hybrid-compatible scanner and write down the freeze frame data
2. With the connector unplugged, check whether the signal wire is making contact with ground.
3. Make sure the battery cooling air intake is clean
4. Check the 12 V auxiliary battery, which can also trigger warnings
5. Leave any high-voltage measurements to a specialized repair shop

Good to know

• Repair difficulty: hard
• It can trigger limp mode.

What each character of P0A0C means

• P: Powertrain: engine and transmission
• 0: Generic code: same on every make
• A: Hybrid or air and fuel
• 0C: Specific fault in that system

Frequently asked questions

Can I keep driving with code P0A0C?

If the car still runs, drive as little as possible and go to a specialized repair shop. Do not touch the orange cables: they carry high voltage.

What causes code P0A0C?

The most common causes are: hV connector, cover or service disconnect open, interrupting the loop; interlock wire shorted to ground, e.g. chafed at a module or the body; corroded or pushed-back interlock pins.

Related codes

• P0A0AHigh Voltage System Interlock Circuit A
• P0A0BHigh Voltage System Interlock Circuit A Performance
• P0A0DHigh Voltage System Interlock Circuit A High
• P0A0EHigh Voltage System Interlock Circuit A Intermittent
• P0D17Battery Charging System A High Voltage Interlock Circuit Low

Sources

• gsi.ext.gm.com: 16OBDG02 Hybrid Diagnostics
• gsi.ext.gm.com: 11OBDG01 HYBRID Diagnostics
• static.nhtsa.gov: MC 11026830 0001

Values and procedures vary by manufacturer. If it affects brakes, steering, fuel or high voltage, see a professional. Updated: 2026-11-04. How we build these pages.